ProblemA_284.cpp

#include<iostream>
using namespace std;
int main()
{
	int n,x;
	cin>>n>>x;
	int init=1;
	long long int sum=0;
	while(n--)
	{
		int l,r;
		cin>>l>>r;
		int num=(l-init)/x;
		int curr=num*x+init;
		sum+=(r-curr)+1;
		init=r+1;
	}
	cout<<sum;
	return 0;
}